Multi-electrolytic cells



'Dec. 7, 1965 G. E. EDWARDS MULTI-ELEGTROLYTIC CELLS 3 Sheets-Sheet 1Filed March 5, 1959 IN VENTOR George Ernesf- Ezwards, y M f A T TORNEYS.

Dec. 7, 1965 G. E; EDWARDS MULTI-ELECTROLYTIC CELLS Filed March 5, 19593 Sheets-Sheet 2 IO ll If?! [VIP l I l: illll- 1/1I/1/I111/1111111 1 II91111 11/11/12 FlG.3

FIG. 2

INVENTOR George Ernesf Edwards, WW M 1' MW ATTORNEYS".

Dec. 7, 19 65 V EDWARDS 3,222,270

MULT I ELECTROLYTI C CELLS Filed March 5, 1959 3 Sheets-Sheet 5 01IOHIOII II/II 1/1,

Fl6.4 FIG-.5

INVENTOR Z G eorge E rn esl' Edwards,

BYMW, M W

A TTORNEYSI United States Patent M 3,222,27 0 MULTI-ELECTROLYTIC CELLSGeorge Ernest Edwards, Widnes, England, assignor to Imperial ChemicalIndustries Limited, London, England, a corporation of Great BritainFiled Mar. 3, 1959, Ser. No. 796,856 Claims priority, application GreatBritain, Mar. 18, 1958, 8,7 15/ 58 15 Claims. (Cl. 204-469) The presentinvention relates to improvements in or relating to multi-electrolyticcells and particularly to multi-electrolytic cells of the kind adaptablefor the production, of for example, chlorine, a hypochlorite or achlorate from aqueous solutions of a chloride of an alkali metal forexample sodium chloride and comprising a plurality of unit electrolyticcells.

Multi-electrolytic cells arev known, for instance, wherein the anode ofone unit cell is separated from the cathode of an adjacent unit cell bya partition of non-conducting inert material, for example concrete, andwherein said anode and said cathode are connected electrically byelectro-conducting connections passing through said partition. Ifdesired these cells may be so constructed, for instance, that each unitcell has a conventional type of asbestos diaphragm placed between itsanode and cathode to prevent the products formed at the anode andcathode from mixing and so to permit these products to be collected.

The object of the present invention is to employ an electro-conductingchemically inert partition in the form of titanium metal sheet as achemically inert partition which separates the anode of one unitelectrolytic cell from the cathode of an adjacent unit electrolyticcell.

According to the present invention a multi-electrolytic cell of the kindadaptable for the production of for example chlorine, a hypochlorite ora chlorate from aqueous solutions of a chloride of an alkali metal, forexample sodium chloride and comprising a plurality of unit electrolyticcells and wherein an inert partition sep arates the anode of one unitelectrolytic cell from the cathode of an adjacent unit electrolytic cellis characterised in that the inert partition is a chemically inertpartition of titanium metal sheet.

The term titanium metal sheet includes a metal sheet of a titanium alloyconsisting essentially of titanium.

In accordance with one embodiment of the invention a multielectrolyticcell is so constructed that each unit cell has a diaphragm, for instancea conventional type of asbestos diaphragm, between its anode and cathodeto permit for instance caustic sodaand chlorine to be collected.However, the diaphragm between the anode and the cathode of each unitcell may comprise a cationic exchange resin.

In accordance with a second embodiment of the invention the anode ineach unit cell is of graphite and at least a portion of that face of thetitanium metal sheet which faces the anode has a layer of a noble metalof the platinum group.

By the term a noble metal of the platinum group is meant ruthenium,rhodium, palladium, osmium, iridium or platinum, or an alloy of two ormore of such metals (hereinafter called generically a platinum metal).

In accordance with a third embodiment of the inven tion the anode ineach unit cell is of graphite treated to be impermeable to chlorine andat least a portion of that face of the titanium metal sheet which facesthe anode has a layer of a metal of high electrical conductivity,

3,222,270 Patented Dec. 7, 1965 In accordance with a fourth andpreferred embodiment of the invention in each unit cell the anode is alayer of a platinum metal which is on one side of the titanium metalsheet and the cathode is that opposed side of the next titanium metalsheet which is free from a layer of a platinum metal.

In said fourth and preferred embodiment of the invention the layer of aplatinum metal can be a film or surface coating of a platinum metalsecured or deposited on one side of the titanium metal sheet in anyconvenient manner. The coating of a platinum metal may be constituted,if desired, by a thin sheet or foil which is welded to the titaniummetal sheet. However, it is preferred for the layer of the platinummetal to be electrolytically deposited on the titanium surface since inthis way a given weight of the platinum metal can be spread over agreater surface of titanium metal sheet. If desired, other methods maylikewise be utilised for applying the coating of the platinum metal tothe titanium metal sheet, for example, roll-bonding, cathode sputtering,vacuum deposition, metal spraying, rolling a platinum metal powder intothe surface of the titanium metal sheet and coating of a titanium metalsheet with a platinum-bearing preparation and subsequently heating asfor example in the manner practised in the ceramic industry.

In said second to fourth mentioned embodiments of the invention eachunit cell may, if desired, be provided with a diaphragm and means forrecycling anolyte and/ or catholyte through the respective compartmentsof each unit cell may also be provided.

Furthermore, if desired, a multi-electrolytic cell of the invention canconsist of mercury unit cells so as to permit sodium amalgam to becollected from its cathodes and chlorine from its anodes.

Multi-electrolytic cells of the invention have the followinlgadvantages.

The replacement of non-conducting inert material, for example concrete,by thin titanium sheets makes the multi cell more compact.

Titanium is extremely resistant to chlorinated brine.

Titanium sheet permits quick assembly operations.

The overall weight of a battery of multi-electrolytic cells of theinvention is much less than a battery of multi-electrolytic cellswherein in each multi-electrolytic cell the partition between the anodeof one unit cell and the cathode of an adjacent unit cell is ofnon-conducting inert material, for example concrete.

In a multi-electrolytic cell of the invention there are no perviousjoints between the anode of one unit cell and the cathode of an adjacentunit cell.

In so far as the first three aforementioned embodiments are concerned itcan be pointed outthat the titanium sheet can be compressed firmly,against for instance a graphite plate and so give good electricalcontact between the anode of one unit cell and the cathode of anadtrical contact in the multi-electrolytic cell of the inven-' tionwithout this cell being under a high degree of com: pression.

The fourth-mentioned embodiment of the invention has the advantage thatit is even more compact than the first three mentioned embodiments, thatthe distance between the anode and cathode of any one unit electrolyticcell is constant while the multi-electrolytic cell of the invention isin operation and that chlorine discharged at the anode is free fromcarbon dioxide.

When a multi-eleetrolytic cell according to this fourth and preferredembodiment of the invention is supplied with saturated sodium chloridesolutions and is connected to a suitable source of direct electriccurrent, chlorine and caustic soda are produced at current efficienciescomparable to those of conventional diaphragm cells having graphiteanodes and asbestos diaphragms supported on steel gauze cathode screens.When operated at a current density of 1.5v ka. per m. of cathode area at85 C. for a period of 8 weeks the chlorine product contains less than0.4% of impurities, of which 0.2% is oxygen. The depleted sodiumchloride solution which leaves the cell contains 120 grams of sodiumhydroxide per litre of solution.

A comparison at given current densities of the mean unit cell voltagesfor a diaphragm multi-electrolytic cell incorporating means forrecycling anolyte and catholyte according to said fourth and preferredembodiment of the invention and for a commercial diaphragm cell of thekind aforementioned is given in the following table.

Four embodiments of a diaphragm multi-electrolytic cell according to theinvention are illustrated by way of example in the diagrammatic drawingsaccompanyinging the provisional specification. FIGURE 1 represents across-section of said four aforementioned embodiments of the invention.FIGURES 2 and 3 represent different views of one embodiment in whicheach unit electrolytic cell comprises a graphite anode, a cathode and aconventional asbestos diaphragm which separates the anode from thecathode and in which a titanium plate separates the graphite anode ofone unit electrolytic cell from the cathode of an adjacent unitelectrolytic cell. FIGURE 4 represents, with respect toFIGURE 1, oneview of an embodiment in which electrical connection between a graphiteanode of a unit electrolytic cell and a titanium metal sheet whichseparates said graphite anode from the cathode of an adjacent unitelectrolytic cell is provided by a thin layer ofa metal of highelectrical conductivity deposited on the whole or part of those faces ofthe titanium plate which would otherwise be in directcontact with thegraphite anode. Said graphite anode, in'accordance with anotherembodiment of the invention, hasbeen treated to make it impervious tochlorine andchlorinated brine. FIGURE 5 represents, with respectto'FIGURE 1, one view of an embodiment of a diaphragm multi-electrolyticcell according to the invention in which each unit electrolytic cellcomprises as anode a thin coating of a platinum metal which is on oneside of a titanium metal plate, a cathodic surface on the opposed sideof the corresponding titanium metal plate of an adjacent unitelectrolytic cell and an intervening conventional asbestos diaphragmsupported on a metal gauze screen in good electrical contact with saidcathodic surface of the titanium metal plate and in which except at theends a titanium plate having on one side thereof a layer of a platinummetal separates the platinum metal layer anode of the unit electrolyticcell on one side thereof from the cathode of the adjacent unitelectrolytic cell on the other side thereof.

Referring more specifically to FIGURES 1 to 3, FIG- URES 2 and 3represent vertical part sections of the first-mentioned embodiment of amulti-electrolytic cell according to the invention through AA and BBrespectively in FIGURE 1, which in turn represents the verticalcross-section of a unit electrolytic cell through C-C in FIGURE 2.

Graphite anodes 1 are held in position against titanium plates 2 byclamping plates 3 of mechanically strong and corrosion resistantmaterial, for example rubber covered steel. There are intervening sheets4 of flexible material such as natural or synthetic rubber between thetitanium plates 2 and the clamping plates 3. 5 are highly compressedportions of the flexible sheets 4 positioned between the adjacent edgesof the graphite anodes 1 and the clamping plates 3. The thickness of theflexible sheets 4 is such that when the multi-electrolytic cell is heldtogether under a suitable degree of of compression the graphite anodes 1are held firmly against the titanium plates 2. 6 are conventionalasbestos diaphragms and these are supported on metal gauze screens 7which are set in metal plates 8. Thin layers 9 of suitable corrosionresistant material are bonded by conventional means to these faces ofthe metal plates 8 which face towards the graphite anodes 1. Thegraphite anodes 1 are maintained at a suitably small distance from theasbestos diaphragm 6 by frames 10 of corrosion resistant materials.Additional frames 11 of corrosion resistant material separate the metalplates 8 from the adjacent titanium plates 2 of adjacent unitelectrolytic cells. Frames 11 differ from frames 10 in their thicknessand in that they are reversed laterally with respect to frames 10, Thetitanium plates 2 are provided with a series of embossed nipples 12which are disposed regularly over those portions of the titanium plates2 which face the metal gauze screens 7. These embossed nipples 12protrude towards the metal gauze screens 7 for such a distance that whenthe multi-electrolytic cell is held together under a suitable degree ofcompression the nipples 12 are in sufiiciently close contact with themetal gauze screens 7 that there is negligible resistance to the flow ofelectrical current between the metal gauze screens 7 and the adjacentfaces of the titanium plates 2. Should it be necessary this resistancecan be reduced by welding together the metal gauze screens 7 and thetitanium plates 2. The metal gauze screens 7 and the adjacent faces ofthe titanium plates 2 form together the cathodes of themulti-electrolytic cell.

The titanium plates 2, the clamping plates 3, the flexible sheets 4, theframes 10, the metal plates 8 and the frames 11 are each provided withfour corresponding apertures 13, 14, 15 and 16 to form ducts 17, 18, 19and 20 respectively. The apertures 13, 14, 15 and 16 in the titaniumplates 2 and the metal plates 8 are enlarged to allow the insertion ofbushes 21 of corrosio resistant and electrically insulating material.These bushes 21 are sealed to the titanium plates 2 and the metal plates8' by a suitable adhesive composition (not shown).

The frames 10 are provided with rectangular apertures 22 of suchdimensions as will conform closely to the dimensions of the graphiteanodes 1 and the asbestos diaphragms 6. These aperture are connected tothe diagonally opposite apertures 13 and 14 by channels 24 and 25respectively. Frames 11 have rectangular apertures 23 of similardimensions to apertures 22 in frames 10. Apertu-res 23 are connected tothe diagonally opposite apertures 15 and 16 respectively by channels 26and 27.

In this embodiment of a multi-electrolytic cell of the invention thecomponents for a suitable number of unit electrolytic cells arepositioned as aforementioned and are held together under a suitabledegree of compression by conventional means. The seals between adjacentcomponents are effected by conventional methods as for example byintervening films of suitable adhesive materials or by thin layers offlexible jointing compounds (not shown). Alternatively the frames and 11may be of suitable flexible material when no further means of sealingare required other than compression. 28 and 29 are current leads to theanode and cathode titanium end plates 2. The rectangular apertures 22 inthe frames 10 form anode compartments which are connected to the ducts17 and 18 by channels 24 and 25 respectively. Similarly the rectangularapertures 23 in the frames 11 form cathode compartments which areconnected to the ducts 19 and by the channels 26 and 27 respectively.The duct 18 serves for the introduction of sodium chloride solution intothe anode compartments 22 through the channels by means of suitableexternal connections (not shown). If this solution is controlled at alevel 30 there will be at least a partial flooding of the duct 17. If,however, the solution is controlled at level 31 there is no flooding ofthe duct 17. The sodium chloride solution percolates through theasbestos diaphragm 6 into the cathode compartment 23 attaining acontrolled level. If the sodium chloride solution is controlled at alevel 32 there will be partial flooding of the duct 19. The solutionthen leaves the multi-electrolytic cell by the channels 27 and the duct20 through suitable external connections (not shown). Should thesolutionbe controlled at a level 33 there is no flooding of the duct 19.

If desired means can be provided for the return of the anolyte from duct17 to duct 18 and/or of the catholyte from duct 19 to duct 20 and forthe circulation of the anolyte and catholyte respectively through theapertures 22 and the apertures 23.

During electrolysis the chlorine which is liberated at the graphiteanodes 1 passes through the channels 24 and the duct 17 and leaves themulti-electrolyti-c cell by suitable external connections (not shown).The hydrogen which is liberated at the composite cathode formed by themetal gauz'e screen 7 and the titanium plate 2 leaves themultielectrolytic cell by the channels 26 and the duct 19 throughsuitable external connections (not shown) while the sodium hydroxidewhich is formed in the cathode compartment 23 leaves themulti-electrolytic cell together with the depleted sodium chloridesolution by the channels 27 and the duct 20 as aforementioned.

FIGURE 4 represents those two embodiments of the invention wherein goodelectrical connection between the graphite anodes 1 and the titaniumplates 2 is obtained by a thin layer 34 of a metal of high electricalconductivity which is deposited, either chemically or electrically, onthe whole or parts of those faces of the titanium plates 2 which wouldotherwise be in direct contact with the graphite anodes 1. The layers 34may either be a platinum metal or a less noble metal, for examplecopper. If the layers 34 are of a less noble metal this metal may beprotected from corrosion by impregnating those parts of the graphiteanode 1 adjacent to the metal layer 34 with an inert material so as torender said parts of the graphite anode 1 completely impervious to thegases or liquids contained in the multi-electrolytic cell. If the layers34 are a noble metal such as platinum no such protection is necessary.

FIGURE 5 represents a v'ertical part section through amulti-electrolytic cell corresponding to a section through A--A inFIGURE 1. In the embodiment of the invention illustrated in FIGURE 5there are no graphite anodes 1, no clamping plates 3, and no flexiblelayers 4. Those faces, however, of the titanium plates 2 which areadjacent to the asbestos diaphragm 6 are provided with a thin coating ofa platinum metal. This thin coating 35 is deposited on the titaniumplates 2 either chemically or electrolytically to form the anodic partof this embodiment of a multi-electrolytic cell according to theinvention.

What I claim is:

1. A multi-electrolytic cell comprising a plurality of unit electrolyticcells, each unit electrolytic cell having an anode and a cathode, saidunit electrolytic cells being arranged with the anode of one unitelectrolytic cell juxtaposed to the cathode of the next unitelectrolytic cell with an inert partition separating the anode of oneunit electrolytic cell from the cathode of the adjacent unitelectrolytic cell, each inert partition being a chemically inertelectroconducting partition of titanium metal sheet, each of saidtitanium metal sheets having on one surface an electrically conductinglayer which is in electrical contact with said titanium sheet overessentially all of said titanium surface, said layer constituting theanode in each unit electrolytic cell, the other surface of each saidsheet comprising titanium and constituting the cathode of the nextadjacent unit electrolytic cell, said anode and cathode constituting thesole essential working electrodes in each said unit cell.

2. A multi-electrolytic cell as claimed in claim 1 wherein each unitcell has a diaphragm between its anode and cathode.

3. A multi-electrolytic cell as claimed in claim 2 wherein the diaphragmis an asbestos diaphragm.

4. A multi-electrolytic cell as claimed in claim 2 wherein the diaphragmcomprises a cationic exchange resin.

5. A multi-electrolytic cell as claimed in claim 1 wherein the anode ineach unit cell is graphite, and essentially all of the surface of thetitanium metal sheet which carries the anode has a layer of a noblemetal of the platinum group providing electrical contact between saidsheet and said anode, the opposite face of said titanium sheetcomprising the cathode of the adjoining cell with the titanium as thecathodically operative surface.

6. A multi-electrolytic cell as claimed is claim 1 wherein the anode ineach cell is graphite rendered impermeable to chlorine and essentiallyall of the surface of the titanium metal sheet which carries the anodehas a layer of a metal of high electrical conductivity which forms goodelectrical contact both with the titanium metal sheet and the graphite,the opposite face of said titanium sheet comprising the cathode of theadjoining cell.

7. A multi-electrolytic cell as claimed in claim 1 wherein the anode isgraphite applied directly to said one surface of said titanium metalsheet.

8. A multi-electrolytic cell as claimed. in claim 6 wherein the metal ofhigh electrical conductivity which forms good electrical contact bothwith the titanium metal sheet and the graphite is selected from thegroup consisting of copper, silver, and platinum.

9. A multi-electrolytic cell as claimed in claim 1 wherein the pluralityof unit electrolytic cells are mercury unit cells.

10. A multi-electrolytic cell of the bipolar electrode filter-press typefor the electrolysis of alkali metal chlorides and comprising aplurality of unit electrolytic cells, each unit electrolytic cell havingan anode and a cathode, said unit electrolytic cells being arranged withthe anode of one unit electrolytic cell juxtaposed to the cathode of thenext unit electrolytic cell with an inert partition separating the anodeof one unit electrolytic cell from the cathode of the adjacent unitelectrolytic cell, each inert partition being a chemically inertelectroconducting partition of titanium metal sheet, each of saidtitanium metal sheets having on one surface a layer of a platinum metal,said layer constituting the anode in each unit electrolytic cell, theother surface of each said sheet comprising titanium as the operativesurface and constituting the cathode of the next adjacent unitelectrolytic cell, said anode and cathode constituting the soleessential working electrodes in each said unit cell.

11. A multi-electrolytic cell as claimed in claim 10 wherein the layerof platinum metal is a film of a platinum metal secured on one side ofthe titanium metal sheet.

12. A multi-electrolytic cell as claimed in claim 11 wherein the film ofa platinum metal is a thin sheet or foil which is welded to the titaniummetal sheet.

13. A multi-electrolytic cell as claimed in claim 10 wherein the layerof platinum metal is a surface coating of a platinum metal deposited onone side of the titanium metal sheet.

14. A multi-electrolytie cell as claimed in claim 13 wherein the surfacecoating of a platinum metal is an electrolytic deposit on the titaniumsurface.

15. A multi-electrolytic cell as claimed in claim 13 wherein the surfacecoating of a platinum metal on the titanium surface is a subsequentlyheated coating of a platinum bearing preparation,

References Cited by the Examiner UNITED STATES PATENTS Baum 2049-290Niederreither 204256 Gunn et al. 204256 Suggs et al. 204290 Rosenblatt204290 Zdansky 204256 Tirrell 204290 JOHN H. MACK, Primary Examiner.

JOHN R. SPECK, Examiner.

1. A MULTI-ELECTOLYTIC CELL COMPRISING A PLURALITY OF UNIT ELECTROLYTICCELLS, EACH UNIT ELECTROLYTIC CELL HAVING AN ANODE AND A CATHODE, SAIDUNIT ELECTROLYTIC CELLS BEING ARRANGED WITH THE ANODE OF ONE UNITELECTROLYTIC CELL JUXTAPOSED TO THE CATHODE OF THE NEXT UNITELECTROLYTIC CELL WITH AN INERT PARTITION SEPARATING THE ANODE OF ONEUNIT ELECTROLYTIC CELL FROM THE CATHODE OF THE ADJACENT UNIT ELECTROLTYECELL, EACH INERT PARTITION BEING A CHEMICALLY INERT ELECTROCONDUCTINGPARTITION OF TITANIUM METAL SHEET, EACH OF SAID TITANIUM METAL SHEETSHAVING ON ONE SUFACE AN ELECTRICALLY CONDUCTING LAYER WHICH IS INELECTRICAL CONTACT WITH SAID TITANIUM SHEET OVER ESSENTIALLY ALL OF SAIDTITANIUM SURFACE, SAID AYER CONSTITUTING THE ANODE IN EACH UNITELECTROLYTIC CELL, THE OTHER SURFACE OF EACH SAID SHEET COMPRISINGTITANIUM AND CONSTITUTING THE CATHODE OF THE NEXT ADJACENT UNITELECTROLYTIC CELL, SAID ANODE AND CATHODE CONSTITUTING THE SOLEESSENTIAL WORKING ELECTRODES IN EACH SAID UNIT CELL.